/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;
import java.util.List;
import javax.annotation.CheckForNull;

/**
 * An ordering that compares objects according to a given order.
 */
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
final class ExplicitOrdering<T> extends Ordering<T> implements Serializable
{
    final ImmutableMap<T, Integer> rankMap;

    ExplicitOrdering(List<T> valuesInOrder)
    {
        this(Maps.indexMap(valuesInOrder));
    }

    ExplicitOrdering(ImmutableMap<T, Integer> rankMap)
    {
        this.rankMap = rankMap;
    }

    @Override
    public int compare(T left, T right)
    {
        return rank(left) - rank(right); // safe because both are nonnegative
    }

    private int rank(T value)
    {
        Integer rank = rankMap.get(value);
        if (rank == null)
        {
            throw new IncomparableValueException(value);
        }
        return rank;
    }

    @Override
    public boolean equals(@CheckForNull Object object)
    {
        if (object instanceof ExplicitOrdering)
        {
            ExplicitOrdering<?> that = (ExplicitOrdering<?>) object;
            return this.rankMap.equals(that.rankMap);
        }
        return false;
    }

    @Override
    public int hashCode()
    {
        return rankMap.hashCode();
    }

    @Override
    public String toString()
    {
        return "Ordering.explicit(" + rankMap.keySet() + ")";
    }

    private static final long serialVersionUID = 0;
}
